Dear student,
3 reasons are as follows -
1) The educated middle-class took got inspired by the french revolution and it was among the educated, liberal middle classes that ideas of national unity following the abolition of aristocratic privileges gained popularity.
2) Napoleonic Code went back to limited suffrage and reduced women to the status of a minor, subject to the authority of fathers and husbands and because of it women and non-propertied men organized opposition movements demanding equal political rights.
3) Conservative regimes set up in 1815 were autocratic. They did not tolerate criticism and dissent, and sought to curb activities that questioned the legitimacy of autocratic governments. Most of the revolutionaries saw the creation of nation-states as a necessary part of this struggle for freedom.
Regards